Thermoplastic ionomers of copolymers of α-olefins, particularly ethylene, and C3-8 α,β ethylenically unsaturated carboxylic acids such as acrylic acid and methacrylic acid offer excellent properties in transparency, chemical resistance, toughness, scratch resistance, gloss, as well as a wide range of processability. They are widely used in packaging and industrial applications. U.S. Pat. No. 3,264,272 teaches methods for making such ionomers. The acid copolymers on which the ionomers are based may be prepared as described in U.S. Pat. No. 4,351,931.
However, stiffness and rigidity of these ionomers drop when the end use temperature is elevated above ambient, especially above 50° C. This property can be quantified as the heat deflection temperature. Low heat deflection temperatures have restricted the use of ionomers in many applications where higher heat deflection temperature and higher stiffness are required.
Ionomers have been modified with nanoclays to increase their stiffness. See U.S. Pat. Nos. 6,919,395, 7,208,546, 7,261,647, and 7,314,896. High complexity is involved in dispersing nanoclay with ionomers in order to achieve high efficacy.
U.S. Pat. Nos. 4,255,322, 4,595,727, 5,362,809 and 5,502,111 disclose blends of PVC with polyglutarimides having improved heat deflection temperatures. The polyglutarimides themselves, also known as imidized acrylic polymers or imides of polyacrylic acids, have been described in U.S. Pat. Nos. 2,146,209, 3,284,425, 4,169,924, and 4,246,374. It is also known to combine imidized acrylic polymers with other materials, such as impact modifiers, pigments, fibers, stabilizers, lubricants etc., as described in U.S. Pat. Nos. 4,246,374 and 4,217,424.
Imidized acrylic resins have also been blended with polyamides (nylons) to improve the melt flow, melt strength, tensile strength, and modulus of polyamides. Compatible polymer blends of polyamides and imidized acrylic resins possess improved impact resistance and ductility compared with neat imidized acrylic resins. The addition of high service temperature imidized acrylic resins to a lower service temperature nylon results in improved service temperature for the nylon. Compatible polymer blends of imidized acrylic resins, nylons, and conventional impact modifiers exhibit an improved response to impact modification than does the imide modified with an equal amount of the conventional impact modifier (see U.S. Pat. Nos. 4,415,706 and 4,874,817).
Imidized acrylic resins with low acid levels have been blended with other thermoplastic polymers to provide improved properties such as better melt viscosity, greater compatibility and/or miscibility, greater weather ability, greater impact resistance, better ductility and better solvent resistance (see U.S. Pat. No. 4,727,117).
Imidized acrylic resins have also been blended with compositions of polyoxymethylene (POM) and thermoplastic polyurethane to provide improvement in mold shrinkage while still maintaining a useful balance of the properties, such as stiffness, elongation, and toughness, that are inherent in the POM/polyurethane composition (see U.S. Pat. No. 5,318,813).
It is desirable to develop ionomer compositions with improved heat resistance properties such as increased Vicat temperature, increased stiffness/modulus at room temperature and at elevated temperatures below the ionomer's melting point, and increased upper use temperature at a given stiffness. It is also desirable to develop compositions with these properties that are easy to prepare and process. Preferably, improving the heat resistance of the ionomer would not come at the expense of deterioration in the other attractive properties of ionomers like toughness (measured by notched izod), abrasion resistance or ability to form strong bonds between adjacent layers of ionomer by the application of heat from a sealing bar (heat seal initiation). Incorporating mineral fillers to improve the heat deflection temperature typically comes at the expense of toughness.